A couple builds I have been working on for a while and some range results from the weekend....
The first is built from DPMS components, 20" Noveske 1:12 twist rifle length gas system chambered in 7.62x39mmUSA, JP adjustable gas block, Leupold M3....25.3 grains of A1680 under a 110 V-Max = 2675fps...25.3 grains of A1680 under a 125 TNT = 2530fps....as far as accuracy I didn't bring any targets with me to the range....centered up on the 200 yard gong 20 rounds made a nice brite spot about the size of a quarter...
The second is built from a combination of DPMS and Olympic components and began life as a 300 fireball....was recently rechambered in 7.62x39mmUSA....the original pistol length gas system under the handguard was removed / plugged and set up as a carbine length system....It's a hoot to shoot with 25 grains of A1680....a little more BOOM than the original fireball loads
The 7.62x39mmUSA compared to 300/221 and .223 Rem
The 7.62x39mmUSA compared to a 300/221 in a mag
The 7.62x39mmUSA is based on a .223 parent case..it uses standard bolt face and mags....as in my 300 fireball barrel, I hand re-chambered it with the longer reamer.....here is an old thread from 07 talking about the development
http://www.quarterbore.net/forums/showthread.php?t=1481
I left a reamer and headspace gauges with John Noveske if anyone is interested in having a barrel cut.....PTG also has the print on file....Its been a little work getting there and the only powder I have tried is the A1680 but I guess thats part of the fun....